I've been a ponder since 1998. I recently experienced something that I hadn't before; a fish die off. I lost 4 6-7 inch goldfish in one day and then one or two more on the subsequent days. My large Koi seemed fine and the small goldfish appeared healthy as well. I've never lost this many fish in such a short time for what appeared to be health reasons. (Snakes and GBH yes but that's another topic. The weekend before I'd cleaned out my Bio-Falls filter, washed off the Matala pads, spun plastic filter pads and 4 bags of lava rock and bio-balls as I usually do once a year. The water was crystal clear, pond was looking good and then the fish began to die. Initially, I took it as an unfortunate coincidence and then it continued. Then, I thought that it might have been because the daily high temperature had jumped up about 20 degrees from what it had been. (What happened to Spring?) A friend of mine suggested that I test the water. Me test!? I was beyond that. Hadn't done a water test in 3 or 4 years. Things were fine, or so I thought. I dug out my box of test kits and began testing: Ammonia - 0. Oxygen - great. Ph - 6.0! How'd that happen? At one time years back I'd used some Ph Down but I never had to raise the Ph. I did a water change and brought it up a little. I did others on the following two weeks. Ph is up now and the fish seem fine; no more deaths. I used to do water changes but I'd not been doing them as regularly as I'd done in the past. I guess I need to do them a little more regularly, huh?